Erythropoietin (EPO) is a very important agent for the treatment of anemias associated with compromised EPO production, advanced cancer and chemotherapy. EPO plays essential role in stimulating the growth and differentiation of erythroid progenitors during erythropoiesis. Although EPO has wide clinical applications, little is known about its mechanism of action. Exactly how it regulates growth and differentiation is poorly understood. It is the goal of this proposal to understand how EPO's binding to its receptor(s) leads to the induction of genes such as oncogenes associated with growth and differentiation. EPO has been shown to alter protein phosphorylation on serine through activation of PK-C. Preliminary studies have demonstrated that EPO also modulates tyrosyl phosphorylation, stimulates JUN/AP-l enhancer activity, induces c-jun mRNA expression and activates PK-C. Activation of both PK-C and JUN/AP-l sequence by PNA and growth factors are associated with regulation of differentiation. In this proposal, we will examine (l) whether EPO activates JUN and FOS RNA and protein synthesis; (2) whether EPO modulates the levels of genes associated with cell cycle regulation; (3) whether EPO activates transcription through the AP-l site; (4) identify signal transduction molecules involved in mediating EPO's signal to the nucleus and (5) the relationship between PK-C activation, stimulation of c-jun expression and induction of differentiation by EPO. The knowledge which will be obtained from this project will enable us to use EPO more effectively in the treatment of human diseases including cancer and to block its activity when it functions to promote growth of neoplastic cells.